Electric lighting accounts for approximately 40 percent of all energy consumed in modern buildings. Incorporating available daylight can reduce these annual energy costs by 40 to 50 percent using “daylight harvesting” techniques. The basic principle of daylight harvesting is to monitor the amount of daylight entering an interior space and dim the electric lighting as required to maintain a comfortable luminous environment for the occupants. Where required, motorized blinds and electrochromic windows may also be employed to limit the amount of daylight entering the occupied spaces. Further energy savings can be realized through the use of occupancy sensors and personal lighting controls that operate in concert with the daylight harvesting system. These systems can be onerous to model and control using current methods, and rely on extensive computing resources to adequately model and control the variables involved.
Three-dimensional virtual representations of architectural and theatrical lighting systems were first developed in the 1980s, and today are often used by architects and lighting designers to both visualize and analyze their daylighting and electric lighting system designs. Architectural and theatrical lighting systems are not limited to interior lighting, and include lighting systems on the exterior of buildings or structures.
A typical workflow for the creation of said virtual representations comprises the steps of: 1) using a computer-aided drafting (CAD) program to create a three-dimensional representation of the geometry of a building or similar architectural environment; 2) assigning material properties such as color, transparency, and texture to the geometric surfaces; 3) specifying the photometric properties of light sources within the environment; 4) calculating the distribution of direct and indirect illumination due to the light sources within the environment; and 5) displaying the virtual representations on a computer monitor or other visual display medium.
Calculation of the distribution of direct and indirect illumination is typically performed using global illumination techniques such as those described in, for example, “The State of the Art in Interactive Global Illumination” (Ritschel et al., 2011, Computer Graphics Forum 31(1):160-168). Critically for the photometric analysis of lighting designs (including both electric lighting and daylight), these techniques are based on the physical principles of light interaction with surfaces and materials, rather than mere artistic representations.
Most global illumination techniques are based on ray tracing, including those techniques known as irradiance caching, photon mapping, and multidimensional light cuts. The advantage of ray tracing techniques is that they can accurately model reflections from specular and semispecular (“glossy”) surfaces, refraction by transparent materials such as glass and water, interactions with participating media such as smoke and fog, and subsurface translucency of human skin, marble, and so forth. These features are critically important for the generation of high quality “photorealistic” imagery, including both still images and motion pictures.
One of the disadvantages of ray tracing techniques is that they are view-dependent; a specific position and view direction within the virtual environment must be chosen in order to trace rays to and from the virtual camera. The various ray tracing techniques are computationally expensive, typically necessitating the distribution of direct and indirect illumination within the environment to be calculated offline using minutes to days of CPU time. (While it is possible to approximate the appearance of direct and indirect illumination within an environment in real time for computer games, the resultant images are unsuitable for photometric analysis as required by architects and lighting designers.)
The view dependency of ray tracing techniques further means that only those surfaces visible in the rendered images are available for photometric analysis. For an architectural building with multiple rooms, for example, one or more rendered images must be generated for each room.
Not all global illumination techniques are based on ray tracing; there is also a class of finite element methods referred to as “radiosity.” These methods are more commonly used in thermal engineering to model radiative flux transfer between surfaces, but they are equally capable of modeling reflections from diffuse and semispecular surfaces, and transmission by transparent and translucent surfaces, as described in, for example, “Radiosity: A Programmer's Perspective” (Ashdown 1994. New York, N.Y.: John Wiley & Sons). While less capable of generating high quality photorealistic imagery, they are ideally suited for photometric analysis. In addition to the calculated illuminance distributions being physically accurate, they are view-independent. Once the calculations have been completed, the entire three-dimensional environment can be interactively viewed and photometrically analyzed in real time without the need for further calculations.
A particular disadvantage of both ray tracing techniques and radiosity methods, however, is that they are incapable of generating representations of “dynamic” lighting systems in real time. Examples of such lighting systems include theatrical and entertainment lighting where the intensity and color of the light sources is continuously varied, and architectural lighting systems where the light sources may be dimmable or have varying color temperatures (e.g., “warm white” to “cool white”). Another example is daylighting, where it may be desirable to display and analyze the distribution of daylight in architectural spaces throughout the year.
Theatrical and entertainment lighting systems in particular may have tens to hundreds, and even thousands, of lighting “channels” wherein each channel dims one or a plurality of electric light sources (“luminaires”). Three such channels may be assigned to color-changing luminaires with red, green, and blue light sources. Architectural lighting systems are similar, albeit with only a few lighting channels to dim the luminaires and possibly change their color temperatures.
If possible, lighting designers would like to have the ability to both visualize and photometrically analyze these electric lighting and daylighting system in a virtual environment as a design tool. Ideally, it should be possible (especially for theatrical and entertainment lighting systems) to interactively control the lighting channel settings while interactively viewing the three-dimensional environment.
One prior art approach has been to specify a fixed virtual camera position and view direction, then generate a multiplicity of static images wherein for each image, exactly one of the lighting channels is set at full intensity while the other channels are disabled. These images are then blended in real time during display to simulate the effect of dimming the different lighting channels. This approach is mostly limited, however, to the representation of simple architectural dimming system, as each lighting channel requires a full-resolution still image. A theatrical lighting system with hundreds to thousands of lighting channels would overwhelm the graphics capabilities of most desktop computers, not to mention the more limited capabilities of tablet computers and smartphones.
Another prior art approach relies on the real-time display capabilities of graphics hardware subsystems such as OpenGL from Khronos Group and Direct3D from Microsoft. Commercial software products such as, for example, WYSIWIG from Cast Software, enable lighting designers to visualize theatrical lighting systems with hundreds to thousands of lighting channels controlled by physical lighting consoles that are connected to a desktop computer. The disadvantage of this approach is that, while the 3D virtual environment can be interactively viewed, only the direct illumination from the luminaires can be modeled; indirect illumination due to interreflections from surfaces (which can often constitute over half of the illumination in an enclosed environment) is necessarily ignored. Further, the luminous intensity distributions of the luminaires—a critical aspect of professional lighting design—can only be approximated using the real-time capabilities of the graphic hardware subsystems. The resultant renderings are schematic rather than physically accurate.
There is therefore as need for a system and method of real-time dynamic lighting simulation, wherein a photometrically accurate representation of an environment can be displayed and analyzed in real time, while a plurality of hundreds to thousands of lighting channels may have their intensity settings being continually varied and the user may interactively view the three-dimensional environment, all without the need for ongoing global illumination calculations. The system and method should further be suitable for implementation on a variety of platforms, ranging from desktop computers to smartphones with bandwidth-limited communications.